1. Field of the Invention
The present invention relates to in-pile creep test systems and, more particularly, to a remote-controlled in-pile creep test system used in in-pile tests for measuring and determining mechanical properties of nuclear materials irradiated in research reactors.
2. Description of the Prior Art
As well known to those skilled in the art, a variety of in-pile creep tests or so-called materials irradiation tests have been performed in research reactors in order to measure or determine the integrity of nuclear materials irradiated in the reactors, in the procedure of developing new nuclear materials.
Particularly, creep tests for structural nuclear materials, such as the materials for clad tubes or pressure vessels, must be performed under irradiation in research reactors.
In-pile creep test systems for performing such creep tests in research reactors are each installed in the reactor core containing distilled water, so the systems must have high structural and operational stability and reliability.
In addition, the in-pile creep test systems must be designed such that they are usable for testing irradiated nuclear materials having various sizes and shapes, such as materials having cylindrical shapes, plate-type shapes or rod-type shapes, and have structures capable of allowing sufficient and constant irradiation to specimens, and are easily manipulated in the reactors.
Furthermore, the in-pile creep test systems must be disassembled by remote-controlled manipulators in hot cells after creep tests, and be reduced the number of their disassembled parts, thus reducing the amount of nuclear wastes.
Capsule-type creep test systems for creep tests in research reactors have been typically classified into several types, that is, non-instrumented capsule-type systems without having any testing instrument in the capsules, instrumented capsule-type systems having various testing instruments in the capsules, and special instrumented capsule-type systems, which are capable of measuring mechanical properties of irradiated materials. In the field of creep tests, such capsule-type test systems are typically referred to simply as xe2x80x9cnon-instrumented capsulesxe2x80x9d, xe2x80x9cinstrumented capsulesxe2x80x9d and xe2x80x9cspecial instrumented capsulesxe2x80x9d, respectively.
In order to perform a materials irradiation test using a creep test system, an operator installs a specimen of a target material in a predetermined unit of the capsule, prior to assembling the units of the test system into a single structure. In such a case, some units are welded in the capsule, thus being fixed to the capsule.
In a materials irradiation test using a special instrumented capsule-type system, creep strain is measured while applying tensile load or compressive load or repeated cyclic loading to an irradiated specimen so as to form creeps on the specimen for accomplishing the object of the test for measuring and determining mechanical properties of the irradiated specimen.
Therefore, several additional instruments, such as measuring instruments, must be installed in the capsule of such a special instrumented capsule-type system, so it is almost impossible to use the capsule of a conventional non-instrumented capsule-type system or of a conventional instrumented capsule-type system as the capsule of a special instrumented capsule-type system.
The instruments, such as measuring instruments, which are installed in the capsule of a special instrumented capsule-type system must be designed and fabricated while considering the following factors: That is, the instruments do not affect the exposure dose of irradiation to a specimen in a capsule, and allow an application of tensile or compressive load or repeated cyclic loading to the specimen, and minimize the amount of nuclear wastes generated by the disassembled parts of the test system after a creep test.
In such a capsule-type creep test system, some units are welded in the capsule, so it is necessary to design the system such that the capsule is easily cut and disassembled in a hot cell after a creep test. In addition, a bellows, an LVDT (linear variable differential transducer) etc. are irradiated during a creep test, so it is almost impossible to reuse them. However, it is desired to carefully disassemble the irradiated units, such as the bellows and LVDT, so as to prevent damage to the units in an effort to avoid breakage of a specimen after a creep test.
The creep test system is also designed and fabricated such that it is possible to avoid any damage or breakage of the specimen during a procedure of disassembling the irradiated specimen from the test system after a creep test.
The special instrumented capsule-type creep test system is installed in a research reactor, so the system must have high structural stability and reliability, and can be compatibly used in measuring and determining mechanical properties of various irradiated materials.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an in-pile creep test system, which is used in an in-pile creep test for measuring mechanical properties of nuclear materials irradiated in a research reactor, and which is designed to be remote-controlled.
In order to accomplish the above objects, the present invention provides an in-pile creep test system, comprising: a creep tester vertically installed in the reactor pool of a nuclear reactor, and used in a tensile or compressive or low cyclic fatigue creep test; a detecting unit electrically connected to the creep tester, and used for detecting a temperature of the tester and creep strain of a specimen installed in the tester; a gas supply unit connected to the creep tester through gas supply tubes, and controllably supplying helium gas from a helium gas reservoir tank to the tester or returning helium gas from the tester to the tank by an operation of an air compressor and a vacuum pump; and a control unit electrically connected to both the detecting unit and gas supply unit so as to control an operation of the creep test system in response to results of a comparison of input data from the detecting unit and the gas supply unit with stored data, whereby the creep tester has simple structure for the convenience of installing speimen and assembling parts and also is easily cut and disassembled in a hot cell, and prevents damage or breakage of the specimen during a procedure of removing the specimen from the tester after a creep test, and is used for performing creep tests for specimens having a variety of shapes and sizes.
The creep tester comprises: a fixing unit fixed to the reactor pool so as to vertically install the creep tester in reactor pool; a pressurizing unit pressurized or depressurized by compressed helium gas fed into a chamber defined in the creep tester at a position adjacent to the fixing unit; a movable unit for applying tensile load, compressive load or repeated load to the specimen in response to an operation of the pressurizing unit; a heating unit assembled with the movable unit and used for heating the specimen; a measuring unit for detecting a movement of the movable unit so as to measure creep strain of the specimen; and a cylindrical capsule consisting of a plurality of capsule parts, with the fixing unit being mounted to an end of the capsule, and the pressurizing unit, movable unit, heating unit and the measuring unit being sequentially housed in the capsule.
The fixing unit comprises: a base plate provided at an end of the capsule; a fixing shaft axially projecting from a center of the base plate; a stop plate movably fitted over the fixing shaft; and an elastic member provided between the base plate and the stop plate so as to bias the stop plate in a predetermined direction.
The pressurizing unit comprises: a first plate fixedly set in the capsule at a position spaced apart from the base plate at a predetermined interval, and defining the chamber; a bellows tube mounted to the first plate at a position inside the chamber; a push plate integrally mounted to an end of the bellows tube so as to selectively push the movable unit.
The first plate has a central opening through which the push rod of the movable unit movably passes.
A push rod slot is formed on the push plate so as to allow a push rod of the movable unit to come into precise contact with the push plate.
The movable unit comprises: a first holder unit set at a position adjacent to a first plate of the pressurizing unit, and divided on the basis of a central axis of the capsule into two parts which are spaced apart from each other by a predetermined gap; and a second holder unit assembled with the first holder unit while being partially overlapped with the first holder unit, the second holder unit being movably assembled with a first guide stopper which is set in the capsule at a position spaced apart from the first plate of the pressurizing unit by a predetermined distance.
The first holder unit comprises: a guide slot formed along the central axis of the capsule; an upper holder plate formed at an upper portion around the guide slot, and having a plurality of upper locking holes; and a lower holder plate formed at a lower portion around the guide slot so as to face the upper holder plate, and having a plurality of lower locking holes.
The second holder unit comprises: a push rod having a predetermined length and movably passing through a central hole of the first plate; a U-shaped specimen holding rod coupled to an end of the push rod so as to hold the specimen; a cylindrical holder pipe connected to an end of the U-shaped specimen holding rod and having a plurality of upper and lower locking holes so as to hold the specimen with the use of locking pins inserted in the upper and lower locking holes; and a slide shaft connected to an end of the cylindrical holder pipe and movably passing through the central opening of the first guide stopper.
The slide shaft has a probe-seating slot at a center of an end surface thereof, such that a probe of a strain-measuring instrument, such as a linear variable differential transducer, is precisely arranged along the central axis of the capsule.
A bearing member is set in the central opening of the first guide stopper so as to movably bear the slide shaft in the first guide stopper while preventing frictional contact between the first guide stopper and the slide shaft.
The heating unit comprises: a cylindrical heater housing, with an axial slit formed at a sidewall of the heater housing so as to allow the heater housing to be fitted over the U-shaped specimen holding rod of the movable unit from a side of the U-shaped specimen holding rod; a plurality of tube-seating grooves axially formed on an external surface of the heater housing so as to allow the gas supply tubes to pass along the external surface of the heater housing; and a heater made of silicon carbide and set in the sidewall of the heater housing, and electrically connected to the detecting unit.
The measuring unit comprises: a strain-measuring instrument, such as a linear variable differential transducer (LVDT), axially passing through the center of a second guide stopper in the capsule such that the strain-measuring instrument is axially aligned with a slide shaft of the movable unit held by a first guide stopper; and a fixing cap assembled with an end of the strain-measuring instrument, and attached to an end surface of a third guide stopper mounted in the capsule.
The capsule is a cylindrical body consisting of: a first capsule part for supporting the fixing unit, and housing the pressurizing unit while defining the chamber, with a first plate being welded to an internal surface of the first capsule part so as to hold the pressurizing unit in the first capsule part; a second capsule part assembled with an end of the first capsule part and housing the movable unit, with a first guide stopper being welded to an inner surface of the second capsule part so as to hold the movable unit in the second capsule part; a third capsule part assembled with an end of the second capsule part and housing the measuring unit, with a second guide stopper being welded to an inner surface of the third capsule part so as to hold the measuring unit in the third capsule part such that the measuring unit is aligned with a central axis of the third capsule part; a fourth capsule part assembled with an end of the third capsule part and housing a fixing cap of a strain-measuring instrument, with a third guide stopper being welded to an inner surface of the fourth capsule part so as to hold the fixing cap in the fourth capsule part; and a sealing capsule part having a plurality of porous sealing plates assembled with an end of the fourth capsule part so as to seal the fourth capsule part through which electric wires for both the heating unit and the measuring unit are led into the capsule and the gas supply tubes are led from the gas supply unit into the capsule, whereby the capsule parts are isolated from each other and independently sealed, so even though there is breakage or damage to a part of the creep tester, the breakage or damage is not propagated to another part, but is limited to the originally broken or damaged part, thus improving structural stability and operational reliability of the creep tester.
In the in-pile creep test system, the detecting unit is electrically connected to the control unit, the heater of the heating unit, the LVDT or the strain-measuring instrument, thus detecting a temperature of the heating unit and creep strain of the specimen.
The gas supply unit is electrically connected to the control unit, and communicates with the air compressor, a vacuum pump, and a helium gas reservoir tank through tubes, and is connected to the chamber of the pressurizing unit through the gas supply tubes.
The in-pile creep test system of the present invention performs a desired creep test for irradiated materials with the use of the special instrumented capsule type creep tester installed in a reactor pool containing distilled water.
That is, in order to perform a tensile creep test, the creep tester is vertically installed on the base in the reactor pool by fixing the fixing unit of the tester to the base. During a tensile creep test, the control unit controls the detecting unit in response to stored data, thus activating the heating unit. At the same time, the control unit controls the gas supply unit to feed compressed helium gas to the chamber of the pressurizing unit, thus allowing the pressurizing unit to advance to move the movable unit and creating tensile strain of the specimen installed in the movable unit.
In such a case, the measuring unit, which is in contact with the movable unit, measures the strain of the specimen, and outputs a signal indicative of the creep strain. The control unit thus compares data signals from both the measuring unit and the detecting unit with stored date, and controls the gas supply unit in response to the signal comparison results so as to controllably supply or return helium gas to or from the chamber.
In order to perform a compression creep test, the bellows tube of the pressurizing unit is compressed to the maximum with the use of the gas supply unit during a procedure of assembling the parts of the creep tester into a single structure. During a compression creep test, the helium gas is returned from the chamber to the helium gas reservoir tank under the control of the control unit, thus depressurizing the chamber and simultaneously the helium gas is supplied to the second capsule part to effectively pull the movable part. The pressurizing unit is thus retracted to create compressive strain of the specimen. In an effort to enhance a depressurizing effect of the chamber as well as allowing an easy retraction of the movable unit during such a compressive creep test, a spring may be installed on the push rod of the movable unit.